Modified rosin esters and their use in printing inks

ABSTRACT

A binder for use in gravure printing ink formulations comprising a modified rosin ester resinate prepared by forming a rosin-dienophile adduct, reacting the adduct with a polyfunctional hydroxy compound to form an ester and reacting with an acrylic-containing polymer to form a hard rosin ester. The polymer-modified rosin ester resinate is formed by reacting the prepared hard rosin ester with a rosin-dienophile adduct and an acrylic-containing polymer, reacting the product thereof with reactive zinc, followed by a reaction with lime, dehydrating the resinate product by refluxing, and adjusting its viscosity with a hydrocarbon solvent.

BACKGROUND OF THE INVENTION

(1) Field Of The Invention

The present invention relates to rosin ester resins modified with ahydroxy functional polymer, such as an acrylic polymer. Morespecifically, this invention relates to acrylic polymer modified estersof rosin, methods for preparing the modified rosin, as well as the useof an acrylic polymer modified rosin ester in vehicles for gravureprinting inks.

(2) Description Of The Prior Art

Modified rosins have come into widespread use as binders in vehicles forgravure printing inks. However, these inks are usually quite costly. Inaddition, with the development of the printing arts, the speeds ofprinting have become increasingly high, and requirements for various inkproperties such as gloss, drying properties, blocking holdout, firmformation, film toughness (resistance to abrasion), reducibility andprintability, color development, resistance to static movement or rubare of primary importance to the resin supplier. All of these propertiesare affected by the resin or binder used to formulate these inks.

Prior to this invention rosins have been modified with one or more (insuccession) or with a combination of dienophiles, and/or with phenolicresins and often followed by esterification in attempts to producetougher, glossier inks that are resistant to rub. The beneficial productcharacteristics provided by rosin esters for various uses have led tothe development of many esterification procedures, particularlytreatments with polyhydric alcohols. U.S. Pat. No. 2,369,125 to Jones,et al. and U.S. Pat. No. 2,572,086 and U.S. Pat. No. 2,590,910 each toWittcoff, et al. teach rosin esterification with glycerol andpentaerythritol, among other polyhydric alcohols

In U.S. Pat. No. 2,478,490 to Krumbhaar, there is disclosedrosin-modified, phenol/formaldehyde resins containing rosin esterifiedby polyhydric alcohols and reinforced by polybasic acids of the maleictype which are useful in printing inks These rosin-modifiedphenol/formaldehyde resins and rosin-modified maleic esters are preparedby heating rosin together wit phenol/formaldehyde condensates, withmaleic-type polybasic acids, or both, and subsequently esterifying withpolyhydric alcohol.

Japanese Patent 62-265,376 to Toray Ind. discloses printing inkcompositions containing rosin modified phenolic resins with apolyfunctional acrylate. The Japanese patent does not disclose amodified resin that has been esterified. U.S. Pat. No. 4,693,846 toPiccirilli, et al. discloses a urethane-modified dimerized rosin esterfor use in lithographic printing inks an coatings.

There exists a need in the art of gravure printing for an ink which isinexpensive and exhibits good properties in such parameters as filmtoughness (resistance to abrasion), blocking, color development, gloss,resistance to static movement or rub, high hold out and excellentprintability when printed on a given substrate. All of these propertiesare affected by the resin or binder used to formulate the ink.

Accordingly, it is a primary object of this invention to provide rosinresins and resinates which produce superior gravure printing inks andavoid unsatisfactory physical properties

Another object of this invention is to provide improved modified rosinresins and resinates for use in printing ink formulations.

Yet another object of this invention to provide a process for makingmodified rosin resins and resinates which are particularly useful as acomponent of printing ink vehicles.

It is a further object of this invention to provide a gravure printingink containing a modified rosin or resinate as a binder which exhibitsimproved film toughness, gloss and Sutherland rub.

Other objects, features and advantages of the invention will be apparentfrom the details of the invention as more fully described and claimed.

SUMMARY OF THE INVENTION

The present invention is a modified rosin prepared by forming an adductof rosin and a dienophile, reacting the rosin adduct with apolyfunctional hydroxy compound to form an ester and reacting the esterwith an acrylic-containing polymer to form a hard resin. In analternative embodiment, a resinate is formed from the hard resinintermediate by blending the reaction product of a rosin adduct, acopolymer, and the hard resin, followed by reaction with zinc in ahydrocarbon solvent. The present invention also includes a gravureprinting ink having a vehicle comprising, as the binder, a modifiedrosin ester resin or resinate of this invention in a hydrocarbon solventand a pigment dispersed therein.

It has been found that the gravure printing ink formulations inaccordance with this invention have significant increases in rubresistance, abrasion and high gloss, and provide quality printing.

DETAILED DESCRIPTION OF THE INVENTION

The rosins employed in this invention may be tall oil rosin, gum rosin,or wood rosin. Rosin is mainly a mixture of C₂₀, fused-ring,monocarboxylic acids, typified by levopimaric and abietic acids, both ofwhich are susceptible to numerous chemical transformations.

Tall oil rosin is isolated from crude tall oil obtained by acidulationof the "black liquor soap" skimmed off the concentrated alkalinedigestion liquor washed out of paper pulp in the kraft, i.e. sulfate,pulping process for making paper. Fractionation of the crude tall oilyields tall oil rosin and fatty acids. The tall oil rosin used in thisinvention generally contains at least about 80% rosin acids, preferablyat least about 85% to 88% rosin acids, and most preferably about 95% to97% rosin acids. It should be understood, however, that the inventioncontemplates the use of tall oil rosin having rosin contents much lower,for example, about 30% rosin acids. The remaining material is fattyacids and unsaponifiable material

Gum rosin is produced by the nature separation and gradual conversion ofsome of the hydrophilic components of sap and related plant fluids fromthe cambium layer of a tree into increasingly hydrophobic solids. Pinegum contains about 80% gum rosin and about 20% turpentine.

Wood rosin is obtained by resinification of oleoresin from eithernatural evaporation of oil from an extrudate or slow collection in ductsin sapwood and heartwood. Pine tree stumps are valuable enough to beextracted with hexane or higher-boiling paraffins to yield wood rosin,wood turpentine, and other terpene-related compounds by fractionaldistillation.

To produce the hard resin intermediate for resinate production, rosin ischarged to a reactor and heated until melted, usually about 180° C. Thereaction can be conducted in a vessel properly equipped with athermometer, stirrer, and a distillation column to separate water thatdistills from reactants, and, optionally, a Dean-Stark trap. The moltenrosin is agitated as soon as the melting process makes it possible, andagitation is continued throughout the process.

A dienophile is added to the molten rosin, and the mixture is heated tocause a Diels-Alder (cycloaddition) reaction between the dienophile andthe rosin. The preferred dienophiles for reaction with the rosincomponent are fumaric acid, maleic acid, acrylic acid, methacrylic acid,itaconic acid, citraconic acid and maleic anhydride. It is possible tosubstitute other dienophiles therefor although they are less preferred.Preferably, the dienophiles are used in an amount of from about 3% toabout 20% by weight of rosin and, more preferably, comprises from about5% to about 15% by weight of rosin.

The reaction temperature should be in the range of between the meltingpoint of the rosin and the boiling point of the dienophile. Thus, theoptimum reaction temperature will be selected depending upon the rosinand the dienophile used, generally from about 150° C. to about 250° C.,with from about 200° C. to about 210° C. being preferred. Heating iscontinued until a rosin adduct is produced having an acid number of fromabout 210 to about 220, which usually takes from about 1 to about 3hours. The reaction may be carried out under a blanket of inert gas,such as nitrogen.

Upon completion of the reaction, the rosin adduct is reacted with apolyfunctional alcohol and the acrylic-containing polymer to form amodified rosin ester resin.

The rosin adduct is also reacted with an acrylic-containing polymer.Typical acrylic-containing polymers include a polymer mixture of acrylicacid, methacrylic acid, or one or several of their organic esterderivatives, and a member selected from the group consisting of styrenealpha methyl styrene, ethylene vinyl acetate, and a combination thereof.A preferred polymer is styrene-acrylic polymer, such as Joncryl® 587,available from S. C. Johnson. Generally, from about 10% to about 50% byweight of the acrylic-containing polymer, preferably from about 20% toabout 40%, is reacted.

The reaction can be conducted most successfully at temperatures of 200°C. to 300° C., preferably about 200° C. to about 210 C., until a desiredacid value and/or hydroxyl value is attained. Lower temperature can beemployed, but the rate of reaction will be slowed thereby. Also, highertemperature can be employed, but temperatures above the point at whichdistillation of reactants or the final product result will affect yielddeliteriously. Solvents such as azeotropic solvents such as toluene orxylene or high boiling hydrocarbons can be employed. Catalysts such ascondensation catalysts, e.g., dibutyltin oxide or butyl stannoic acid,can also be employed in the reaction. The reaction can be conducted in avessel properly equipped with a thermometer, stirrer, a distillationcolumn to separate water that distills from reactants, and, optionally,a Dean-Stark trap.

In the preparation of the rosin esterification product, polyfunctionalhydroxy compounds are reacted with the rosin adduct. The polyfunctionalhydroxy compounds useful herein are preferably polyhydric alcohols. Thepolyhydric alcohols are preferably high functional polyols. By highfunctional polyols, it is meant those polyols containing more than twohydroxyl groups which will react with the acid functional reactants toproduce rosin esters having high softening points and good dilutabilitywith hydrocarbon solvents. The polyol may contain substituents, providedthat the substituents do not adversely affect the reaction of thepolyols or the performance of the resultant products. Illustrativeexamples of these polyols are mono- or poly-pentaerythritol such as di-or tri-pentaerythritol. Other examples of the useful polyols aretrimethylolpropane, trimethylolethane, glycerine and the like. Usefulpolyfunctional alcohols include those alcohols containing at least onehydroxyl group and another functional group that can react with the acidfunctional group of the rosin.

In the preparation of the hydroxyl-functional esterification product,the particular reactants and reaction conditions that are used willdictate the particular ratio of reactants. The reactants are employed insuch a ratio that the resultant esterification product ishydroxyl-functional. Typically, the equivalent ratio of the acidfunctional reactant to the polyol can be from about 0.8:1.2 to 1:1.2.

The polyfunctional hydroxy compound and a defoamer, if needed topreclude excessive foaming, is charged to the reaction vessel by mixingthe polyfunctional hydroxy compound with the catalyst and dividing themixture into several equivalent portions which are added uniformly overa limited time period while the temperature in the reaction vessel isheld above about 180.C , preferably above about 185° C. After additionof the polyfunctional hydroxy 8 compound and, optionally, an alkalinecatalyst, the reaction vessel is heated to from about 200° C. to about275° C., preferably about 200° C. to about 210° C., uniformly over aperiod of about three hours. This heating is designed to maximize theesterification of the rosin resin. Uniform heating minimizes sublimationof the polyfunctional hydroxy compound. Heating is continued at the sametemperature until an acid number of 155 is reached.

The resultant polymer-modified ester of rosin generally has gooddilutability in appropriate hydrocarbon solvents. The physicalproperties of the modified rosin ester resin made by the process of thepresent invention include:

    ______________________________________                                        Acid Number       145-155                                                     Melt Point(°C.)                                                                          110-120                                                     Viscosity (50% in Toluene)                                                                      P-T (Gardner scale)                                         Color (50% in Toluene)                                                                          10 max.                                                     ______________________________________                                    

The invention resinate is formed by making a rosin-dienophile adduct,preferably by heating the rosin with maleic anhydride at about 160° C.for an hour. Paraformaldehyde may be added to accelerate the reaction.

To the rosin-dienophile adduct are added an acrylic-containingcopolymer, in an amount from about 10% to about 50% by weight of rosinadduct, and the polymer-modified ester of rosin prepared above, in anamount from 2% to about 10% by weight of rosin adduct, and the mixtureis blended.

The blend is reacted with a slurry of a reactive zinc compound dissolvedin a hydrocarbon solvent. Suitable reactive zinc compounds includemetallic zinc or oxides or hydroxides of zinc. The reaction temperaturedepends upon the rosin adduct and the reactive zinc compound, generallyat under reflux or at temperatures from about 200° to about 280° C. Thereaction can be accelerated using a catalyst, such as, dibutyltin oxideor butyl stannoic acid. The desirable amount of the zinc compound, basedon the adduct, is the reaction equivalent or less. Generally, from about2% to about 8% by weight, particularly from about 4% to about 7% byweight, based on the weight of the rosin adduct of zinc is reacted. Itshould be understood that magnesium oxide and/or calcium hydroxide(lime) may replace part or all of the zinc in this reaction. Hydrocarbonsolvents, such as those generally used as vehicles in printing inks maybe used to form the hydrocarbon slurry.

Another aspect of this invention is to form a solution rosin resinateutilizing the good dilutability characteristics of the modified rosinester resinate. A convenient method is to dissolve the resinate into ahydrocarbon solvent, such as benzene, toluene, xylene, and mixturesthereof, in situ. The amount of hard resin which will dissolve will varydepending upon the solvent used.

The resinates of this invention generally have good dilutability inhydrocarbon solvents and, preferably, exhibit the following properties:

    ______________________________________                                        Bulk Viscosity 25° C. (Brookfield, Cps)                                                       2000-4000                                              Color, Gardner         10-17                                                  % Non-Volatiles        45-65                                                  Gardner Viscosity, 25° C.                                                                      R-Z2                                                  Melt Point, ° C.                                                                              170-235                                                Acid Number            40-70                                                  ______________________________________                                    

The printing inks formulated in accordance with the present inventioninclude the modified rosin ester resinate dissolved in an organicsolvent as the printing ink vehicle. These printing inks are made in thesame manner as conventional printing inks except the resin of thepresent invention is employed in the ink vehicle. Optionally, the inksmay include other ingredients which are typically used in printing inks.The pigments used in the printing inks are well-known to those ofordinary skill in the printing art.

The ink compositions generally are prepared by dispersing, pigment,clay, hydrocarbon solvent, metalated resinate, lecithin and a smallamount of an organic compound in a mill. This dispersion is reduced witha mixture of conventional resinate, cellulose, alcohol solvent,hydrocarbon solvent, and the resin vehicle of the present invention toproduce an excellent printing ink particularly suitable for use inpublication gravure printing.

The most common mixing ratio of the vehicle, pigment and reinforcingfiller is as follows:

    ______________________________________                                                       Desirable                                                                            Optimum                                                                Extent Extent                                                  ______________________________________                                        Vehicle (wt. parts)                                                                            60-97    80-90                                               Pigment (wt. parts)                                                                             3-40    10-20                                               ______________________________________                                         The mixing ratio may be varied according to the use of the ink, so that     the present invention is not intended to be limited to the above ranges.

These resin/resinates when used as either grind-type or let down-typevehicles, or both, in inks offer significant increases in rub, abrasion,and gloss with no detriment to other pertinent properties of the inkfilm. Abrasion resistance, as measured on a Taber Abrasion Tester, mayincrease by 200-300% when used at equal amounts against moreconventional resin/resinates. Sutherland Rub Test also shows increasesof 50-100% with 10% increase in gloss as well as equal blocking.

The following examples are provided to further illustrate the presentinvention and are not to be construed as limiting the invention in anymanner. All parts are parts by weight unless otherwise stated.

EXAMPLE 1

A hard resin precursor was formed by adding to a suitable reactionkettle under a nitrogen blanket, 10,000 pounds of tall oil rosin. Therosin was heated to 170° C. and the nitrogen turned off, at which time1,000 pounds fumaric acid was added. The reaction mixture was heated at210° C. for about two hours (until a clear pill was formed) to form acomplete rosin adduct. To the rosin adduct was added 150 ml of DCAAntiform and 3,350 pounds of acrylic-styrene polymer (Joncryl 587) andthe heat maintained for 15 minutes. Four pounds of lime was added andthe mixture held at 195° C. for one hour. Two hundred pounds ofglycerine was added and heating continued at 205° C. until an acidnumber of 155 was reached.

EXAMPLE 2

A resinate modified with a modified rosin resin was produced by reactingrosin and maleic anhydride at 160° C. for one hour in the presence of asmall amount of paraformaldahyde to accelerate the reaction. To themaleic rosin adduct, dissolved in toluene, was blended an ethylene vinylacetate copolymer and 5% by weight of the hard resin precursor fromExample 1. This mixture was cooled to 90° C. and a slurry containingZnO/MgO was reacted, followed by reaction with lime to form theinvention resinate. The temperature of the resinate was increased toreflux, and the resinate dehydrated. The physical properties of thisproduct are:

    ______________________________________                                        Color, Gardner     12-13                                                      Dilution           102 ml/100 gm                                              % Non-Volatile      48                                                        Gardner Viscosity, 25° C.                                                                  Z-Z1                                                      Melt Point, °C.                                                                           190                                                        ______________________________________                                    

The solution resinate of Example 2 was tested for rub, abrasion, andgloss with no detriment to other pertinent properties of the ink film.Abrasion resistance was measured on a Taber Abrasion Tester andincreased 200-300% when used at equal amounts against more conventionalresin/resinates. Sutherland Rub Test also showed increases of 50-100%with 10% increase in gloss as well as equal blocking.

While the invention has been described and illustrated herein byreferences to various specific materials, procedures and examples, it isunderstood that the invention is not restricted to the particularmaterials, combinations of materials, and procedures selected for thatpurpose. Numerous variations of such details can be employed, as will beappreciated by those skilled in the art.

That which is claimed is:
 1. A polymer-modified rosin ester comprisingthe reaction product of: a rosin-dienophile adduct prepared as theproduct of a Diels-Alder reaction of a rosin selected from the groupconsisting of tall oil rosin, wood rosin, and gum rosin and a dienophileselected from the group consisting of fumaric acid, maleic acid, maleicanhydride, acrylic acid, methacrylic acid, citraconic acid, and itaconicacid; a polyfunctional hydroxy compound; and an acrylic-containingpolymer selected from the group consisting of mixtures of: a polymer ofacrylic acid, organic ester derivatives of acrylic acid, methacrylicacid, organic ester derivatives of methacrylic acid, and mixturesthereof; and a member selected from the group consisting of styrene,alpha methyl styrene, ethylene vinyl acetate, and a combination thereof.2. The polymer-modified rosin ester of claim 1 wherein the dienophile ispresent in an amount from about 3% to about 20% by weight of rosin. 3.The polymer-modified rosin ester of claim 1 wherein the dienophile ispresent in an amount from about 5% to about 15% by weight of rosin. 4.The polymer-modified rosin ester of claim 1 wherein the polyfunctionalhydroxy compound is selected from the group consisting ofpentaerythritol, trimethylolpropane, glycerine and mixtures thereof. 5.The polymer-modified rosin ester of claim 4 wherein the polyfunctionalhydroxy compound is present in an amount of from about 1% to about 5% byweight of total rosin ester.
 6. The polymer-modified rosin ester ofclaim 1 wherein the acrylic-containing polymer is a mixture of acrylicacid and a polymer selected from the group consisting of styrene andethylene vinyl acetate.
 7. The polymer-modified rosin ester of claim 1wherein the amount of acrylic-containing polymer is from about 10% toabout 50% by weight of total rosin ester.
 8. The polymer-modified rosinester of claim 7 wherein the amount of acrylic-containing polymer isfrom about 20% to about 40% by weight of total rosin ester.
 9. Apolymer-modified rosin ester comprising:(a) a rosin adduct of tall oilrosin and a dienophile selected from the group consisting of fumaricacid, maleic acid and maleic anhydride; (b) a polyfunctional hydroxycompound selected from the group consisting of pentaerythritol andglycerin; and (c) an acrylic-styrene copolymer.